Field of the Invention
The present invention relates to a constant-velocity joint, which is interposed between a first transmission shaft and a second transmission shaft, for transmitting rotary drive power from the first transmission shaft to the second transmission shaft.
Description of the Related Art
Automobiles are arranged such that rotary drive power, which is generated by an internal combustion engine, an electric motor, or the like, is transmitted to the tires by drive power transmission shafts such as drive shafts, etc. In this case, the automobile is driven when the tires are rotated by the transmitted rotary drive power.
A constant-velocity joint is interposed between the drive power transmission shafts. The constant-velocity joint interconnects the drive power transmission shafts, such that the drive power transmission shafts can rotate about respective axes thereof.
One known type of constant-velocity joint is a tripod constant-velocity joint. Such a tripod constant-velocity joint comprises an outer member having a bottomed cup, and an inner member that is fitted to the distal end of a drive power transmission shaft. Rollers, which are held by holders of the inner member, slide while rotating within respective guide grooves defined in an inner wall surface of the bottomed cup. When the drive power transmission shaft is tilted at a prescribed working angle, the rollers are tilted within the guide grooves in response to the inner member being tilted within the outer member.
Generally, the tripod constant-velocity joint operates by rotating, sliding, and tilting, as described above. When the rollers are tilted, the rollers are restrained by the guide grooves. In the case that the rollers slide while being restrained, slippage occurs between the wall surfaces of the guide grooves and the rollers, thus resulting in an increase in sliding resistance. Sliding resistance also increases when the rollers rotate.
Such increased sliding resistance is responsible for vibration and noise. Japanese Laid-Open Patent Publication No. 2011-501068 (PCT) discloses a constant-velocity joint having roller assemblies, each of which includes an inner roller, and an outer roller, which is mounted on the inner roller through an interposed needle bearing. The inner roller is restrained against rotation by a holder of an inner member.